The present invention broadly relates to a scroll fluid machine having scroll members which make an orbiting motion relative to each other with their spiral wraps meshing with each other so that volumes of working chambers defined by both wraps are progressively varied to compress, expand or transfer a gas, and more particularly, to an oil-free scroll fluid machine in which lubrication is not conducted in the working chambers although bearings and other portions are lubricated.
Japanese Patent Unexamined Publication Nos. 57-131896 and 63-61786 disclose scroll fluid machines in which the position of the center of gravity of the orbiting scroll member and the positional relationship between the center of gravity and the orbiting bearing are suitably determined so as to minimize fluttering and precession of the orbiting scroll member thereby improving the reliability of the orbiting bearing.
The scroll fluid machine disclosed in Japanese Patent Unexamined Publication No. 57-131896, however, is not designed with full consideration of the discharge passage along which a gas is discharged from the machine. Therefore, when this scroll machine is used to compress, expand or transfer a gas at a large flow rate, the discharged gas encounters a large resistance due to restricted volume of the discharge passage. On the other hand, the scroll fluid machine disclosed in Japanese Patent Unexamined Publication No. 63-61786 encounters difficulties in supplying a lubricating oil into the orbiting bearing. In addition, this type of scroll fluid machine is not designed to operate satisfactorily when the ratio of the discharge pressure to the suction pressure is small. It is also to be pointed out that this type of scroll fluid machine is not designed to enable easy maintenance work on the orbiting bearing. Furthermore, a considerably large moment acts on the orbiting scroll member by the gas during operation of the machine.